Blood test identifies people with resistant malaria

OUR old foe malaria is becoming resistant to artemisinin – the world's most potent antimalarial drug. But it may not be too late to turn the tide.

A large study has scoped out the extent of resistance in South-East Asia and shown that a blood test can quickly identify people with resistant malaria. That's crucial information for any attempt to stop its spread, including an ambitious plan to blanket treat the entire population in the drug-resistant heartland.

"If you are planning to create a firewall around resistance, it is essential to know the edges," says Nick White of Mahidol University in Bangkok, Thailand.

Resistance to antimalarial drugs can emerge anywhere they are used, but curiously it has begun in one region a disproportionate number of times. That area is the Greater Mekong – encompassing forests in Burma, Thailand, Cambodia, Vietnam, Laos and Bangladesh.

Researchers suspected that here, the malaria parasite Plasmodium is somehow more easily able to develop the mutations that bring resistance, says Dominic Kwiatkowski of the Wellcome Trust Sanger Institute in Hinxton, UK. Last year a study linked artemisinin resistance in the region to mutations in a Plasmodium gene called kelch13, and unpublished research by Kwiatkowski supports the idea that Plasmodium there is more genetically susceptible to the kelch13 mutation.

Until now, the only way to identify whether people with malaria carried a resistant strain was to closely monitor them over several days of treatment, taking regular blood samples to see how fast the therapy cleared Plasmodium from their system. But White and his colleagues wondered whether a blood test that detects the presence of parasites with the kelch13 mutation in infected people could offer a less labour-intensive way to identify drug-resistant malaria.

They examined 1240 people being treated for malaria in South-East Asia and Africa, and showed that the blood test can be used successfully: mutations in kelch13 were found in almost all cases of resistance (see diagram). The study also revealed some good news: even the most resistant Plasmodium was still susceptible to artemisinin – it just required a longer course of treatment (The New England Journal of Medicine, doi.org/t5z).

That gives hope for the plan of blanket therapy, says White, in which everyone in the region is given antimalarial drugs, whether they are sick or not. Last year his team began two trials involving several thousand people to test the idea, and they want to do more trials in Cambodia and deeper within Burma – although they have not yet received government approval.

The blanket therapy approach is controversial, though, not just because of the vast expense. Mass drug administration across the region would be difficult to implement, says Pascal Ringwald of the World Health Organization. "It's a huge area with millions of people." If not done rigorously, mass treatment might actually drive resistance. Ringwald wants to see results from the first trials before more begin.

But White thinks there is no time to waste. "We have a rapidly closing window of opportunity," he says. "Few people have died from artemisinin resistance so far but when people do start dying it will be too late."

This article appeared in print under the headline "Gene test aids war on drug-resistant malaria"

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